1. Field of the Invention
The present invention relates to a dampening roller and a method for producing the dampening roller. Further, the present invention relates to dampening systems, employing the dampening roller, for a printing apparatus, particularly for an offset printing apparatus.
2. Description of the Prior Art
Conventionally, various dampening systems have been well known, for example "Insatu-Kogaku Binran (Printing Engineering Handbook)" published by Gihoudo Publishing Co., Ltd. dated on May 1, 1983, the first edition and the first issue, referring to from page 694, line 13 to page 695, line 7 and FIGS. 3, 4 and 17 on page 694; and "Offset Printing Apparatus" published by Nippon Printing Newspaper Company dated on Jun. 25, 1984, the first issue, referring to page 116 to page 121.
These conventional documents disclose dampening systems comprising a dampening form roller adjacent to a plate cylinder, a metal roller arranged at the upstream side with respect to the dampening form roller and in contact with it, and a dampening water feeding means such as a combination of a fountain pan and a fountain roller arranged at the upstream side with respect to the metal roller to feed the dampening water onto the metal roller. The dampening form roller is covered with a molleton or a dampening sleeve, or its surface is made of one of various hydrophilic rubber materials to make the dampening water be in an uniform water layer on the plate cylinder surface. The metal roller is provided with a hydrophilic chromium plated layer to allow the dampening water to spread more widely. The metal roller is driven to reciprocally move in the axial direction of the metal roller while the whole printing apparatus is working. The feeding amount of the dampening water to the plate cylinder is controlled by the cooperation between the metal roller and the dampening water feeding means; for example, by adjusting the contact pressure of the fountain roller in the fountain pan with the metal roller, adjusting the contact angle between the fountain roller and the metal roller, adjusting the revolving speed of the fountain roller, or adjusting the opening degree of a feeding nozzle of the water feeding means which is isolated from the metal roller. However, these dampening water feeding mechanisms are somewhat roughly adjusted in comparison with ink feeding mechanisms for feeding ink onto the plate cylinder.
Another type dampening water feeding apparatus was proposed by Japanese Patent Application Laid-Open Publication No. 63-91247 titled "Dampening Water Apparatus". This apparatus comprises a dampening water feeding means including a dampening water fountain, a fountain roller, and a doctor roller; a vibrator roller arranged at the upstream side of the fountain roller; a dampening roller arranged in contact with the vibrator roller and a circumferential surface of a plate cylinder; and a metering-cum-reserving roller which is in contact with the vibrator roller and isolated from the plate cylinder. The doctor roller is swingingly moved between the fountain roller and the vibrator roller to feed the dampening water from the fountain roller to the vibrator roller. Every rubber-made surface of the doctor roller, the dampening roller and the metering-cum-reserving roller is roughed by abrasion with an abrading wheel, laser-engraving or stamping. These roughed surfaces ensure the formation of an uniform water layer on the plate cylinder so as to produce prints with a high quality that are free from ghost and fuzz caused by dampening water, and further to reduce time for washing on changing color.
The dampening systems disclosed in the former conventional documents "Insatsu-Kogaku Binran" and "Offset Printing Apparatus" hereinafter referred to as "the former conventional devices" need some requirements to apply the dampening water in an uniform water layer onto the plate cylinder. That is, the chromium plated metal roller should be interposed between the dampening form roller and the dampening water feeding means, and reciprocatingly moved in its axial direction, and the dampening form roller should be covered with a molleton or a dampening sleeve, or the circumferential surface of the dampening form roller should be made of a hydrophilic rubber. However, even if the above requirements are wholly satisfied, the dampening water fed on the plate cylinder is not always formed in an uniform layer. Further, the driving mechanism for reciprocatingly moving the metal roller in its axial direction needs complicated maintenance works, the molleton or the dampening sleeve should be sometimes washed and replaced. As disclosed above, the former conventional devices need some complicated operations which will increase time and cost for operating such apparatus.
On the other hand, another type dampening water feeding apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 63-91247, referred as the later conventional device, employs the dampening form roller provided with a roughed surface to remove the molleton or the dampening sleeve from the dampening form roller, thereby improving the defects caused by the former conventional devices. The later conventional device can also form an essentially uniform water layer on the plate cylinder as well as the former conventional devices. Further the later conventional device includes the metering-cum-reserving roller with the rough surface in addition to the doctor roller which is also provided with the rough surface. This arrangement allows the vibrator roller interposed between the dampening form roller and the doctor roller to be free from the requirement that the vibrator roller is reciprocatingly moved in its axial direction; there is no disclosure on this reciprocating motion in the Publication. Thus, the later conventional device can be free from problems caused by the preciprocating driving mechanism in the former conventional devices. On the contrary, the later conventional device requires the dampening roller, the doctor roller and the metering-cum-reserving roller to keep always predetermined rough condition to perform its purpose. The operator should always watch the abrasion in their roller surfaces while the printing apparatus is operating, and further should often replace the rollers and reproduce the rough surface.